The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Kalynda's dad describes joy of homecoming

The father of a young Sydney woman who was detained in China after being accused of drug smuggling has described how he and his daughter burst into tears when their plane arrived back in Australia.

"When we hit the tarmac in Sydney, we both just cried," Larry Davis said.

His 22-year-old daughter Kalynda Davis had been locked away for a month in a Chinese detention centre after being charged with trying to smuggle 75kg of methamphetamine (ice) to Australia with New Zealand man Peter Gardner.

In a statement released through DFAT on Tuesday Ms Davis's family confirmed she was back home and innocent of the allegations levelled against her.

Mr Davis, a former police officer, says he knew his daughter was innocent and prayed every night the truth would come out.

As soon as he heard Kalynda would be released he flew to China to bring her home to Sydney.

"I prayed for the authorities, that it was dealt with in the way that it was dealt with, and our prayers were answered," Mr Davis told the Western Weekender.

Ms Davis was reported missing by her family in early November.

On the same day, Ms Davis, from Glenmore Park in Sydney's west, and Mr Gardner, who had been living in Richmond on Sydney's north-west fringe, flew from Sydney to Guangzhou in China.

It is believed they were due to return on November 8 before being intercepted by Chinese authorities.

In China, drug trafficking convictions carry the death penalty.

Mr Davis flew to Guangzhou on Saturday to bring home his youngest child.

"When I saw her for the first time, I just collapsed. She didn't know that I was coming either. She kept saying `I'm sorry dad, I didn't do it, I didn't do it, I didn't do it'," he said.

The family also thanked supporters who offered well wishes during the month-long ordeal.

Mr Gardner is believed to still be overseas and possibly facing the death penalty.

The 22-year-old woman only had carry-on luggage, Mr Davis said.

"That's all she had and she was just approached by authorities and asked to come back to the office. Then she found out what was happening and was taken to the detention centre."

Ms Davis was not allowed contact with the outside world, was shackled and had her long, blonde hair cut off.

Her parents were left mostly in the dark.

Mr Davis said the Chinese authorities treated his daughter with respect but said the past month had been horrific.

"I don't know what I have been feeling this past month, it is like I have been brain-dead.

"Think of a parents worst nightmare and multiply it by 10, that's what we went through. I know my daughter, I know my daughter - it was just my worst nightmare."

Ms Davis and Mr Gardner reportedly met on the online dating site Tinder shortly before their departure for China.